Allow a player to set the global background image for all scenes

Hello,
I’m am trying to set up global variable for to allow a player to pick the background image for each scene. The scene would start with a certain background and then the player has an option to change it.

Can someone please be very specific in helping me do this?

the backgrounds/objects are global now, and I did try to create a global group but not sure if I did any of it correctly.

Can you show the global objects and group setup? And can you provide screen shots of the events you have regarding the background selection?